With the advent of the digital telecommunications era, digital communication systems handle a wide array of data traffic generated by a plurality of users and applications. These users and applications generate voice, video, and data traffic that communication systems must communicate simultaneously. To communicate different traffic types simultaneously, digital communication systems must ensure that requirements such as latency (the delay time between the data source and the data destination, throughput (the data bandwidth), and error rate (the frequency of mis-communicated data), are satisfied for each traffic type in order to guarantee a sufficient Quality-of-Service. Satisfying these requirements while communicating different traffic types simultaneously is difficult, however, in light of the fact that each type has its own requirements, thereby placing great demands on communication system design. Thus, there is a high demand for digital communication systems that are able to communicate multiple data traffic types simultaneously while maintaining a sufficient Quality-of-Service.
Distinct types of data traffic can be categorized into two classes according to their requirements. The first class, known as Constant Bit Rate Data, is best represented by voice. Data traffic within the Constant Bit Rate Data class has a number of common features, including a stable data rate, stringent latency requirements, and exact uplink/downlink symmetry for voice applications. The stable data rate is characterized by a constant data stream with minimal variance between minimum and maximum data transmission rates. Stringent latency requirements necessitate data transmission and reception with minimal delay, because delays interfere with the constant data stream and corrupt the data communication.
In contrast, the second data type class, Variable Burst Rate Data, has features dissimilar to Constant Bit Rate Data. Common features among the Variable Burst Rate Data class include variable data rates, loose latency requirements, and a strong uplink/downlink asymmetry. The variable data rates, characterized by a large variance between the minimum and maximum data transmission rates, lead to large peaks and lulls in data communication. The loose latency requirement permits large transmission and reception delays between data packets without corrupting the data stream.
Comparing the Constant Bit Rate Data and Variable Burst Rate Data classes, a number of things are apparent. A communication system communicating Constant Bit Rate Data can have a relatively narrow data bandwidth variance due to the small variance in the data communication rate for Constant Bit Rate Data. This advantage, however, is limited by the strict latency and exact uplink/downlink symmetry requirements for Constant Bit Rate Data, which require the communication system to communicate data without delay. In contrast, a communication system communicating Variable Burst Rate Data can withstand long communication delays of asynchronous data. The large data rate variance of Variable Burst Rate Data, however, requires the communication system to have a wide data bandwidth variance that will withstand large communication rate peaks and lulls.
In attempting to design a communication system that can efficiently transmit both Constant Bit Rate Data and Variable Burst Rate Data from multiple users while guaranteeing a satisfactory Quality of Service, a number of data communication methods have been attempted, including Time Division Multiplexing (TDM)/Time Division Multiple Access (TDMA), Code Division Multiplexing (CDM)/Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), and hybrid systems combining these methods. Unfortunately, TDM/TDMA, CDM/CDMA and FDM/FDMA systems do not effectively communicate Constant Bit Rate Data and Variable Burst Data simultaneously. TDM/TDMA systems can efficiently communicate Variable Burst Data, which can withstand high latency periods and asynchronous uplink/downlink, but cannot efficiently communicate Constant Bit Rate Data, due to small time slot lengths and fixed TDM/TDMA header overhead. CDM/CDMA systems without variable spreading factors eliminate TDM/TDMA latency problems for Constant Bit Rate Data by communicating individual data streams simultaneously in a single time slot, but suffer from high data aggravation limitations due to a large peak-to-average power variance caused by Variable Burst Data. CDM/CDMA systems with variable spreading factors reduce the peak-to-average power and its associated aggregation issues, but introduce power interference issues, as peak Variable Burst Rate Data streams overpower minimum power Variable Burst Rate Data streams and Constant Bit Rate Data streams. FDM/FDMA systems communicate Constant Bit Rate Data and Variable Burst Rate Data, but cannot maintain a sufficient Quality-of-Service because of dynamic bandwidth allocation issues.
In an attempt to compensate for the failings of CDM/CDMA, TDM/TDMA, and FDM/FDMA systems, which communicate Constant Bit Rate Data and Variable Burst Rate Data simultaneously, the prior art has combined CDM/CDMA and TDM/TDMA to form hybrid communication systems. In summary, the prior art involves hybrid CDMA-TDMA systems that boost transmission efficiency by using CDMA to utilize the entire frequency spectrum when transmitting data, and by using TDMA to interleave data transmissions. All of these hybrid CDMA-TDMA methods and systems, however, encode and multiplex data on a per user basis, rather than a per data type basis. As a result, when users transmit Constant Bit Rate Data and Variable Burst Rate Data simultaneously, these systems suffer from limitations and inefficiencies caused by transmitting Constant Bit Rate Data and Variable Burst Rate Data simultaneously. More specifically, in these hybrid CDMA-TDMA systems, Constant Bit Rate Data multiplexed using TDMA experiences delays which degrade signal latency, while Variable Burst Rate Data encoded using CDMA experience aggregation problems caused by a large peak-to-average power variance, and near-far power control problems caused by burst data traffic. Thus, even these hybrid CDMA-TDMA systems fail to provide a sufficient Quality-of-Service to communicate Constant Bit Rate Data and Variable Burst Rate Data simultaneously.